Science: Fresh Air in the Depths

When the submarine Nautilus in Jules Verne's Twenty Thousand Leagues
Under the Sea needed a new air supply, it came to the surface, blew
noisily like a winded whale and filled its reservoirs with two days'
supply of compressed air. This simple system was good enough for the
imaginary Nautilus of 1870, but the real SS(N) Nautilus and her nuclear
sisters of the modern U.S. Navy need better air, and are designed to
stay submerged for months on end. In Naval Research Reviews the Naval
Research Laboratory tells how their little worlds are kept almost as
fresh as a sloop tacking...